KWA M93r NS1 Firing Problem

As the video shows, I'm unsure how to fix this firing problem. I'm wondering if I'd be able to fix it myself since I have some experience taking apart KWA M9s, also if the parts are readily available, or would it be better just to send it into my local airsoft shop to have it fixed instead? The gun is fairly old, and I received it as a gift.

The gun is in poor condition externally and internally. Rust has developed over much of the gun due to the previous owner exposing it to the elements for too long.

It could just be really dirty. Have you cleaned and oiled it recently?

I have, When I first received the gun, it was practically drenched in silicone oil. I've cleaned the gun of it's old gun lube and silicone oil, and reapplied on silicone oil on the springs, spring guide, I've only used green gas on the gun, but the previous owner used propane.